This invention is in the field of plant molecular biology. More specifically, this invention pertains to nucleic acid fragments encoding sucrose phosphate synthase in plants and seeds.
In plants photosynthetically fixed carbon is ultimately converted into two main carbohydrate products, sucrose and starch. Sucrose is the form in which most fixed carbon is exported from the photosynthetic cell. Sucrose is then translocated to various parts of the plant which have a need for this sugar such as regions of active growth and developing seeds or tubers. Sucrose is synthesized in the cytoplasm of photosynthetic cells from the precursor dihydroxyacetone phosphate (DiHOAcP). In the last two steps of sucrose biosynthesis UDP-glucose is converted to sucrose by the successive action of sucrose phosphate synthase (SPS) (E.C. 2.4.1.14) and sucrose phosphatase. By modulating the level of SPS in plants it may be possible to control carbon partitioning in photosynthetic cells. Accordingly, the availability of nucleic acid sequences encoding all or a portion of a sucrose phosphate synthase protein would facilitate studies to better understand carbon partitioning in plants.
Worrell, A. C. et al. ((1991) Plant Cell 3:1121-1130) describe a maize cDNA that encodes a sucrose phosphate synthase as confirmed by the ability of the cloned sequence to direct sucrose phosphate synthesis in E. coli. Additional nucleic acid fragments encoding sucrose phosphate synthase have been isolated by other groups (e.g., U.S. Pat. No. 5,665,892; JP 2000262283).
The present invention concerns an isolated polynucleotide comprising: (a) a first nucleotide sequence encoding a first polypeptide comprising at least 400 amino acids, wherein the amino acid sequence of the first polypeptide and the amino acid sequence of SEQ ID NO:24 have at least 70%, 80%, 85%, 90%, or 95% identity based on the Clustal alignment method, (b) a second nucleotide sequence encoding a second polypeptide comprising at least 435 amino acids, wherein the amino acid sequence of the second polypeptide and the amino acid sequence of SEQ ID NO:28 have at least 70%, 80%, 85%, 90%, or 95% identity based on the Clustal alignment method, (c) a third nucleotide sequence encoding a third polypeptide comprising at least 150 amino acids, wherein the amino acid sequence of the third polypeptide and the amino acid sequence of SEQ ID NO:26 have at least 90% or 95% identity based on the Clustal alignment method, or (d) the complement of the first, second, or third nucleotide sequence, wherein the complement and the first, second, or third nucleotide sequence contain the same number of nucleotides and are 100% complementary. The first polypeptide preferably comprises the amino acid sequence of SEQ ID NO:24, the second polypeptide preferably comprises the amino acid sequence of SEQ ID NO:28, and the third polypeptide preferably comprises the amino acid sequence of SEQ ID NO:26. The first nucleotide sequence preferably comprises the nucleotide sequence of SEQ ID NO:23, the second nucleotide sequence preferably comprises the nucleotide sequence of SEQ ID NO:27, and the third nucleotide sequence preferably comprises the nucleotide sequence of SEQ ID NO:25. The first, second, and third polypeptides preferably are sucrose phosphate synthases.
In a second embodiment, the present invention relates to a chimeric gene comprising any of the isolated polynucleotides of the present invention operably linked to a regulatory sequence, and a cell, a plant, and a seed comprising the chimeric gene.
In a third embodiment, the present invention relates to a vector comprising any of the isolated polynucleotides of the present invention.
In a fourth embodiment, the present invention relates to an isolated polynucleotide fragment comprising a nucleotide sequence comprised by any of the polynucleotides of the present invention, wherein the nucleotide sequence contains at least 30, 40, or 60 nucleotides.
In a fifth embodiment, the present invention relates to a method for transforming a cell comprising transforming a cell with any of the isolated polynucleotides of the present invention, and the cell transformed by this method. Advantageously, the cell is eukaryotic, e.g., a yeast or plant cell, or prokaryotic, e.g., a bacterium.
In a sixth embodiment, the present invention relates to a method for producing a transgenic plant comprising transforming a plant cell with any of the isolated polynucleotides of the present invention and regenerating a plant from the transformed plant cell, the transgenic plant produced by this method, and the seed obtained from this transgenic plant.
In a seventh embodiment, the present invention concerns an isolated polypeptide comprising: (a) a first amino acid sequence comprising at least 400 amino acids, wherein the first amino acid sequence and the amino acid sequence of SEQ ID NO:24 have at least 70%, 80%, 85%, 90%, or 95% identity based on the Clustal alignment method, (b) a second amino acid sequence comprising at least 435 amino acids, wherein the second amino acid sequence and the amino acid sequence of SEQ ID NO:28 have at least 70%, 80%, 85%, 90%, or 95% identity based on the Clustal alignment method, or (c) a third amino acid sequence comprising at least 150 amino acids, wherein the third amino acid sequence and the amino acid sequence of SEQ ID NO:26 have at least 90% or 95% identity based on the Clustal alignment method. The first amino acid sequence preferably comprises the amino acid sequence of SEQ ID NO:24, the second amino acid sequence preferably comprises the amino acid sequence of SEQ ID NO:28, and the third amino acid sequence preferably comprises the amino acid sequence of SEQ ID NO:26. The polypeptide preferably is a sucrose phosphate synthase.
In an eighth embodiment, the present invention relates to a virus, preferably a baculovirus, comprising any of the isolated polynucleotides of the present invention or any of the chimeric genes of the present invention.
In a ninth embodiment, the invention relates to a method of selecting an isolated polynucleotide that affects the level of expression of a sucrose phosphate synthase protein or enzyme activity in a host cell, preferably a plant cell, the method comprising the steps of: (a) constructing an isolated polynucleotide of the present invention or an isolated chimeric gene of the present invention; (b) introducing the isolated polynucleotide or the isolated chimeric gene into a host cell; (c) measuring the level of the sucrose phosphate synthase protein or enzyme activity in the host cell containing the isolated polynucleotide; and (d) comparing the level of the sucrose phosphate synthase protein or enzyme activity in the host cell containing the isolated polynucleotide with the level of the sucrose phosphate synthase protein or enzyme activity in the host cell that does not contain the isolated polynucleotide.
In a tenth embodiment, the invention concerns a method of obtaining a nucleic acid fragment encoding a substantial portion of a sucrose phosphate synthase protein, preferably a plant sucrose phosphate synthase protein, comprising the steps of: synthesizing an oligonucleotide primer comprising a nucleotide sequence of at least one of 60 (preferably at least one of 40, most preferably at least one of 30) contiguous nucleotides derived from a nucleotide sequence selected from the group consisting of SEQ ID NO:23, 25, and 27, and the complement of such nucleotide sequences; and amplifying a nucleic acid fragment (preferably a cDNA inserted in a cloning vector) using the oligonucleotide primer. The amplified nucleic acid fragment preferably will encode a substantial portion of a sucrose phosphate synthase protein amino acid sequence.
In an eleventh embodiment, this invention relates to a method of obtaining a nucleic acid fragment encoding all or a substantial portion of the amino acid sequence encoding a sucrose phosphate synthase protein comprising the steps of: probing a cDNA or genomic library with an isolated polynucleotide of the present invention; identifying a DNA clone that hybridizes with an isolated polynucleotide of the present invention; isolating the identified DNA clone; and sequencing the cDNA or genomic fragment that comprises the isolated DNA clone.
In a twelfth embodiment, this invention concerns a method for positive selection of a transformed cell comprising: (a) transforming a host cell with the chimeric gene of the present invention or an expression cassette of the present invention; and (b) growing the transformed host cell, preferably a plant cell, such as a monocot or a dicot, under conditions which allow expression of the sucrose phosphate synthase polynucleotide in an amount sufficient to complement a null mutant to provide a positive selection means.
In a thirteenth embodiment, this invention relates to a method of altering the level of expression of a sucrose phosphate synthase protein in a host cell comprising: (a) transforming a host cell with a chimeric gene of the present invention; and (b) growing the transformed host cell under conditions that are suitable for expression of the chimeric gene wherein expression of the chimeric gene results in production of altered levels of the sucrose phosphate synthase protein in the transformed host cell.